1. Field of Invention
The present invention relates to the art of a substrate device, such as a thin film transistor (TFT) array substrate device, in which TFTs are formed, a method for manufacturing the same, and an electro-optical device such as a liquid crystal device and an electronic apparatus provided with such a substrate device.
2. Description of Related Art
A substrate device, such as the TFT, has semiconductor layers, such as polysilicon films or amorphous silicon films each including a source region, a drain region, and a channel region on a substrate such as a quartz substrate. Gate insulating films formed of a high-temperature oxide (“HTO”) film, such as a thermal oxide film formed by dry oxidation or wet oxidation, a tetraethyl orthosilicate (“TEOS”) film, or a plasma oxide film, are formed on the surfaces of the semiconductor layers. Gate electrode films can be formed on the gate insulating films to form the TFTs on the substrate. The TFTs are formed in individual pixels in an image display region of an electro-optical device, such as a liquid crystal device, to be used as pixel-switching elements in the TFT-array substrate device. TFTs are also formed in a peripheral region of the image display region to be used as a part of a circuit for driving the substrate device.
Also, N-channel type TFTs, which are excellent in carrier mobility because of electrons as carriers, that is, excellent in switching properties, are commonly created in the image display region. CMOS (complementary) type TFTs formed of a pair of an N-channel type TFT and a P-channel type TFT and driven by a small amount of driving current are commonly created in the peripheral region.
The substrate device where the TFTs are formed in the image display region or the peripheral region is widely used in various electro-optical devices including a liquid crystal device of a TFT active matrix driving method. Additionally, such substrate devices are generally required to have superior electrical properties like high performance and high reliability. In particular, it is required that the TFTs that form the substrate device have a higher performance and higher reliability with respect to leakage current properties, interface state density, and a hot carrier tolerance (that is, the leakage current and the interface state density are lower and the hot carrier tolerance is higher). Of course, it is also required to maintain such excellent transistor properties for a relatively long time.
In order to meet such requirements, it is necessary to efficiently perform an appropriate process, that is, the removal or termination of dangling bonds generated in a crystal grain boundary in the semiconductor layer or an interface between the semiconductor layer and the gate insulating film. This is because the on/off properties of the TFTs deteriorate if the dangling bonds resides. Further, it is necessary to prevent moisture from permeating the gate insulating film that forms the TFT or the interface between the gate insulating film and the semiconductor layer. If moisture permeates such film or interface, the threshold voltage Vth of the TFTs increases. In view of maintaining the excellent properties, it is preferable to remove the above-described inconveniences.
Several technique for solving the above problems are provided in conventional technology. However, considering that it is commonly required that the properties of the TFT be generally and significantly improved, it is difficult to say that the complete technique of solving the problems have been proposed.
Further, such problems matter more in the case where the substrate device corresponds to the TFT-array substrate that forms the electro-optical device such as the liquid crystal device capable of displaying images. It is required that such an electro-optical device displays high quality images and maintains high quality images for a long time, which is significantly dependent on the properties of the TFT on the TFT-array substrate.